Reducing acid gases from streams

ABSTRACT

Methods of reducing acid gas from a stream, comprising contacting the stream with a solvent system comprising a glycerol derivative are described herein. Disclosed herein is a composition comprising a glycerol derivative and an acid gas. A method for sweetening a natural gas stream comprising contacting a solvent system comprising a glycerol derivative with a natural gas stream is described herein.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage application filed under 35 U.S.C. §371 of PCT/US2017/049590 filed Aug. 31, 2017, which claims the benefitof U.S. Provisional Application No. 62/382,847, filed Sep. 2, 2016, bothof which are hereby incorporated herein by reference in theirentireties.

FIELD

The subject matter disclosed herein generally relates to methods andsolvent systems for reducing acid gases from streams.

BACKGROUND

Most discussions of “CO₂ capture and sequestration” (CCS) in recentyears relate to the removal of CO₂ from low partial pressure and lowconcentration post-combustion sources, such as the flue gas of coal- andnatural gas-fired power plants (See Rochelle, Science 325 (2009)1652-1654). However, the removal of CO₂ from high concentration, highpressure sources is a well-established, ongoing, and important needwithin many chemical processes/industries. Removal of CO₂ from rawnatural gas to levels below 2 vol % is necessary to limit pipelinecorrosion and maintain heating value. Separation of CO₂ is also a keycomponent of water-gas shift reactions that produce H₂ and CO₂ from COand H₂O, which is important to NH₃ synthesis and future electric powergeneration from coal or other feedstocks via integrated gasificationcombined cycle (IGCC) processes.

Absorptive (i.e., solvent-based) technologies are the most widely usedand mature processes for CO₂ removal from industrial gas streams. Theselection of an appropriate solvent for CO₂ removal is related to theinlet partial pressure and outlet purity specification. If the inletpartial pressure of CO₂ is low (e.g., flue gas), then a reactive or“chemical” solvent such as aqueous monoethanolamine (MEA) orfunctionalized imidazoles (see e.g., U.S. Pat. No. 8,506,914) can beused. The capacity of a chemical solvent can be limited by theconcentration (e.g., molarity) of active species in solution. However,once the active species has become saturated with CO₂, increased CO₂pressure can result in minimal additional absorption in the chemicalsolvent. If the inlet pressure is high and only “bulk” (˜90%) removal ofCO₂ is required, then a non-reactive or “physical” solvent can beutilized. Physical solvents are typically polar (e.g. non-hydrocarbon)organic solvents with suitable thermophysical properties such as lowviscosity, low vapor pressure, high CO₂ absorption capacity, thermalstability, etc. The capacity of a physical solvent is dependent on thepartial pressure of CO₂ in the gas stream, typically showing a linear(i.e. Henry's Law) relationship.

Relative to chemical solvents which require that chemical bonds bebroken at elevated temperature in order to release the CO₂ andregenerate the solvent, physical solvents typically require much milderheating and/or vacuum (flash) stripping. As the throughput of CO₂ isrelated to the volumetric flowrate of solvent, the process footprintwill be minimized and economics optimized based on the selection of theappropriate class of solvent—chemical or physical. Under certainconditions, hybrid solvents containing amines, water and a polar organicsolvent have also been employed, with Shell's SULFINOL™ as one example.

Among physical solvent processes, the SELEXOL™ process is perhaps themost well-known. SELEXOL™ utilizes dimethyl ethers of poly(ethyleneglycol) (DMPEG) as the working fluid. DMPEG has a very low volatility,high boiling point (275° C.) and moderate viscosity (5.8 cP at 20° C.).It is inexpensively produced from the polymerization of ethylene oxide(oxirane) initiated and terminated respectively by methylating speciessuch as MeOH and CH₃Cl in the presence of a strong base (e.g., NaOMe orNaOH). Other physical solvent processes include Rectisol, Purisol,Morphysorb and Fluor Solvent, which utilize chilled MeOH,N-methylpyrrolidinone (NMP), mixtures of morpholine derivatives andpropylene carbonate (PC) as the respective absorbents.

The conventional unit operation for gas absorption is vertical packed ortrayed-columns, where efficient mass transfer requires a balance betweensufficient interfacial area (promoting gas-liquid contact) and a highvoid fraction (minimizing pressure drop). Although this technology hasbeen in use for over a century, disadvantages include large profiles(e.g., height and footprint) and relatively low surface area to volumeratios (<200 m²/m³). Issues such as foaming and flooding may arise fromthe direct gas-liquid contact.

Hollow fiber membrane contactors (HFMCs) can be an alternative toconventional absorption columns, and may offer significant reductions inthe capital expenditures, footprints and solvent inventory associatedwith gas absorption processes. HFMCs can possess much higher interfacialarea, up to 2000 m²/m³, which can greatly improve mass transfer ratesrelative to packing or trays. Major advantages of membrane contactorsinclude much higher specific surface areas (up to 2000 m²/m³), increasedmass transfer coefficients, reduced solvent inventory, and minimizedprocess footprint. However, performance of HFMCs may be more sensitiveto solvent viscosity in terms of pressure drop down the length of thefiber and reduced mass transfer rates which will necessitate moremembrane area to achieve the desired level of gas absorption. Theseeffects become more pronounced if the solvent is chilled. In thiscontext, DMPEG, the absorption fluid of the SELEXOL™ process, may not bean ideal choice for HFMCs. Advanced physical solvents with low vaporpressure, low viscosity and good CO₂ absorption performance are neededfor the efficient operation of HFMCs. The compositions and methodsdisclosed herein address these and other needs.

SUMMARY

In accordance with the purposes of the disclosed materials, compounds,compositions, and methods, as embodied and broadly described herein, thedisclosed subject matter, in one aspect, relates to compounds andcompositions and methods for preparing and using such compounds andcompositions. In some aspects, the disclosed subject matter relates tomethods for reducing acid gases from a stream, comprising contacting thestream (e.g., a gas stream or a liquid stream) with a solvent systemcomprising a glycerol derivative. The glycerol derivative can befunctionalized by substituting the hydrogen in each hydroxyl functionalgroup in glycerol with a different functional group. In some aspects,the glycerol derivative can be functionalized with an alkyl or alkoxyfunctional group in place of the hydrogen atom in each hydroxylfunctional group.

In some aspects, the disclosed subject matter relates to a solventsystem for reducing acid gas from a stream comprising a glycerolderivative and an acid gas.

Methods for sweetening a natural gas feed stream are also providedherein. The methods comprise contacting the natural gas feed streamcomprising acid gases with a solvent system comprising a glyercolderivative as described herein.

Additional advantages will be set forth in part in the description thatfollows, and in part will be obvious from the description, or may belearned by practice of the aspects described below. The advantagesdescribed below will be realized and attained by means of the elementsand combinations particularly pointed out in the appended claims. It isto be understood that both the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not restrictive.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying Figures, which are incorporated in and constitute apart of this specification, illustrate several aspects described below.

FIG. 1 shows a schematic of a gas solubility apparatus.

FIG. 2 shows a comparison of vapor pressure data for 1,2,3-TMP anddiglyme. 1,2,3-TMP vapor pressure measured in this work (filleddiamonds); Sutter's reported distillation condition for 1,2,3-TMP(hollow diamond); Diglyme vapor pressure measured in this work (filledcircles); Diglyme vapor pressure measured by Stull (hollow circles);COMSOTherm vapor pressure calculation for 1,2,3-TMP (solid line);COSMOTherm vapor pressure calculation for diglyme (dashed line).

FIG. 3A shows the absorption isotherms relating the mole fraction of CO₂in 1,2,3-TMP to the partial pressure of CO₂. Circles=30° C., Squares=45°C., Diamonds=60° C., Triangles=75° C. Dashed lines represent the linearleast squares regression with intercept at origin.

FIG. 3B shows the absorption isotherms relating the mole fraction of CO₂in diglyme to the partial pressure of CO₂. Circles=30° C., Squares=45°C., Diamonds=60° C., Triangles=75° C. Dashed lines represent the linearleast squares regression with intercept at origin.

DETAILED DESCRIPTION

The materials, compounds, compositions, articles, and methods describedherein can be understood more readily by reference to the followingdetailed description of specific aspects of the disclosed subject matterand the Examples and Figures included therein.

Before the present materials, compounds, compositions, articles,devices, and methods are disclosed and described, it is to be understoodthat the aspects described below are not limited to specific syntheticmethods or specific reagents, as such may, of course, vary. It is alsoto be understood that the terminology used herein is for the purpose ofdescribing particular aspects only and is not intended to be limiting.

Also, throughout this specification, various publications arereferenced. The disclosures of these publications in their entiretiesare hereby incorporated by reference into this application in order tomore fully describe the state of the art to which the disclosed matterpertains. The references disclosed are also individually andspecifically incorporated by reference herein for the material containedin them that is discussed in the sentence in which the reference isrelied upon.

General Definitions

In this specification and in the claims that follow, reference will bemade to a number of terms, which shall be defined to have the followingmeanings:

Throughout the description and claims of this specification the word“comprise” and other forms of the word, such as “comprising” and“comprises,” means including but not limited to, and is not intended toexclude, for example, other additives, components, integers, or steps.

As used in the description and the appended claims, the singular forms“a,” “an,” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, reference to “a composition”includes mixtures of two or more such compositions, reference to “anionic liquid” includes mixtures of two or more such ionic liquids,reference to “the compound” includes mixtures of two or more suchcompounds, and the like.

“Optional” or “optionally” means that the subsequently described eventor circumstance can or cannot occur, and that the description includesinstances where the event or circumstance occurs and instances where itdoes not.

By “reduce” or other forms of the word, such as “reducing” or“reduction,” is meant lowering of an event or characteristic (e.g., acidgas in a stream). It is understood that this is typically in relation tosome standard or expected value, in other words it is relative, but thatit is not always necessary for the standard or relative value to bereferred to. For example, “reduces CO₂” means reducing the amount of CO₂in a stream relative to a standard or a control. As used herein, reducecan include complete removal. In the disclosed methods, reduction canrefer to a 10 mol %, 20 mol %, 30 mol %, 40 mol %, 50 mol %, 60 mol %,70 mol %, 80 mol %, 90 mol %, or 100 mol % decrease as compared to thestandard or a control. It is understood that the terms “sequester,”“capture,” “remove,” and “separation” are used synonymously with theterm “reduce.”

It is understood that throughout this specification the identifiers“first” and “second” are used solely to aid in distinguishing thevarious components and steps of the disclosed subject matter. Theidentifiers “first” and “second” are not intended to imply anyparticular order, amount, preference, or importance to the components orsteps modified by these terms.

Chemical Definitions

The term “acid gas” as used herein refers to chemical compounds that arecapable of vaporizing to a significant amount or that exist as a gas atambient conditions with significant quantities of one or more gases thatcan be considered a Lewis Acid. A compound is a Lewis Acid if thecompound can act as an electron pair acceptor. The “acid gases”described herein are found in the streams, such as natural gas feeds.Examples of acid gases include CO₂, CO, COS, H₂S, SO₂, NO, N₂O,mercaptans, H₂O, O₂, H₂, N₂, Cl₂, volatile organic compounds, andmixtures of these.

As used herein, the term “substituted” is contemplated to include allpermissible substituents of organic compounds. In a broad aspect, thepermissible substituents include acyclic and cyclic, branched andunbranched, carbocyclic and heterocyclic, and aromatic and nonaromaticsubstituents of organic compounds. Illustrative substituents include,for example, those described below. The permissible substituents can beone or more and the same or different for appropriate organic compounds.For purposes of this disclosure, the heteroatoms, such as nitrogen, canhave hydrogen substituents and/or any permissible substituents oforganic compounds described herein which satisfy the valences of theheteroatoms. This disclosure is not intended to be limited in any mannerby the permissible substituents of organic compounds. Also, the terms“substitution” or “substituted with” include the implicit proviso thatsuch substitution is in accordance with permitted valence of thesubstituted atom and the substituent, and that the substitution resultsin a stable compound, e.g., a compound that does not spontaneouslyundergo transformation such as by rearrangement, cyclization,elimination, etc. In specific examples, when a moiety is indicated asbeing substituted herein, it can be substituted with one or more groupsincluding, but not limited to, alkyl, halogenated alkyl, alkoxy,alkenyl, alkynyl, aryl, heteroaryl, aldehyde, amino, carboxylic acid,ester, ether, halide, hydroxy, ketone, nitro, silyl, sulfo-oxo,sulfonyl, sulfone, sulfoxide, or thiol groups.

The term “alkyl” as used herein is a branched or unbranched saturatedhydrocarbon group of 1 to 24 carbon atoms, such as methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, pentyl, hexyl, heptyl,octyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, eicosyl,tetracosyl, and the like. The alkyl group can also be substituted orunsubstituted. The alkyl group can be substituted with one or moregroups including, but not limited to, alkyl, halogenated alkyl, alkoxy,alkenyl, alkynyl, aryl, heteroaryl, aldehyde, amino, carboxylic acid,ester, ether, halide, hydroxy, ketone, nitro, silyl, sulfo-oxo,sulfonyl, sulfone, sulfoxide, or thiol, as described below.

Throughout the specification “alkyl” is generally used to refer to bothunsubstituted alkyl groups and substituted alkyl groups; however,substituted alkyl groups are also specifically referred to herein byidentifying the specific substituent(s) on the alkyl group. For example,the term “halogenated alkyl” specifically refers to an alkyl group thatis substituted with one or more halide, e.g., fluorine, chlorine,bromine, or iodine. The term “alkoxyalkyl” specifically refers to analkyl group that is substituted with one or more alkoxy groups, asdescribed below. The term “alkylamino” specifically refers to an alkylgroup that is substituted with one or more amino groups, as describedbelow, and the like. When “alkyl” is used in one instance and a specificterm such as “alkyl alcohol” is used in another, it is not meant toimply that the term “alkyl” does not also refer to specific terms suchas “alkyl alcohol” and the like.

This practice is also used for other groups described herein. That is,while a term such as “cycloalkyl” refers to both unsubstituted andsubstituted cycloalkyl moieties, the substituted moieties can, inaddition, be specifically identified herein; for example, a particularsubstituted cycloalkyl can be referred to as, e.g., an“alkylcycloalkyl.” Similarly, a substituted alkoxy can be specificallyreferred to as, e.g., a “halogenated alkoxy,” a particular substitutedalkenyl can be, e.g., an “alkenylalcohol,” and the like. Again, thepractice of using a general term, such as “cycloalkyl,” and a specificterm, such as “alkylcycloalkyl,” is not meant to imply that the generalterm does not also include the specific term.

The term “alkenyl” as used herein is a hydrocarbon group of from 2 to 24carbon atoms with a structural formula containing at least onecarbon-carbon double bond. Asymmetric structures such as (A¹A²)C═C(A³A⁴)are intended to include both the E and Z isomers. This can be presumedin structural formulae herein wherein an asymmetric alkene is present,or it can be explicitly indicated by the bond symbol C═C. The alkenylgroup can be substituted with one or more groups including, but notlimited to, alkyl, halogenated alkyl, alkoxy, alkenyl, alkynyl, aryl,heteroaryl, aldehyde, amino, carboxylic acid, ester, ether, halide,hydroxy, ketone, nitro, silyl, sulfo-oxo, sulfonyl, sulfone, sulfoxide,or thiol, as described below.

The term “alkynyl” as used herein is a hydrocarbon group of 2 to 24carbon atoms with a structural formula containing at least onecarbon-carbon triple bond. The alkynyl group can be substituted with oneor more groups including, but not limited to, alkyl, halogenated alkyl,alkoxy, alkenyl, alkynyl, aryl, heteroaryl, aldehyde, amino, carboxylicacid, ester, ether, halide, hydroxy, ketone, nitro, silyl, sulfo-oxo,sulfonyl, sulfone, sulfoxide, or thiol, as described below.

The term “aryl” as used herein is a group that contains any carbon-basedaromatic group including, but not limited to, benzene, naphthalene,phenyl, biphenyl, phenoxybenzene, triptycene, and the like. The term“heteroaryl” is defined as a group that contains an aromatic group thathas at least one heteroatom incorporated within the ring of the aromaticgroup. Examples of heteroatoms include, but are not limited to,nitrogen, oxygen, sulfur, and phosphorus. Likewise, the term“non-heteroaryl,” which is also included in the term “aryl,” defines agroup that contains an aromatic group that does not contain aheteroatom. The aryl or heteroaryl group can be substituted orunsubstituted. The aryl or heteroaryl group can be substituted with oneor more groups including, but not limited to, alkyl, halogenated alkyl,alkoxy, alkenyl, alkynyl, aryl, heteroaryl, aldehyde, amino, carboxylicacid, ester, ether, halide, hydroxy, ketone, nitro, silyl, sulfo-oxo,sulfonyl, sulfone, sulfoxide, or thiol as described herein. The term“biaryl” is a specific type of aryl group and is included in thedefinition of aryl. Biaryl refers to two aryl groups that are boundtogether via a fused ring structure, as in naphthalene, or are attachedvia one or more carbon-carbon bonds, as in biphenyl.

The term “cycloalkyl” as used herein is a non-aromatic carbon-based ringcomposed of at least three carbon atoms. Examples of cycloalkyl groupsinclude, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl,cyclohexyl, etc. The term “heterocycloalkyl” is a cycloalkyl group whereat least one of the carbon atoms of the ring is substituted with aheteroatom such as, but not limited to, nitrogen, oxygen, sulfur, orphosphorus. The cycloalkyl group and heterocycloalkyl group can besubstituted or unsubstituted. The cycloalkyl group and heterocycloalkylgroup can be substituted with one or more groups including, but notlimited to, alkyl, alkoxy, alkenyl, alkynyl, aryl, heteroaryl, aldehyde,amino, carboxylic acid, ester, ether, halide, hydroxy, ketone, nitro,silyl, sulfo-oxo, sulfonyl, sulfone, sulfoxide, or thiol as describedherein.

The term “cycloalkenyl” as used herein is a non-aromatic carbon-basedring composed of at least three carbon atoms and containing at least onedouble bound, i.e., C═C. Examples of cycloalkenyl groups include, butare not limited to, cyclopropenyl, cyclobutenyl, cyclopentenyl,cyclopentadienyl, cyclohexenyl, cyclohexadienyl, and the like. The term“heterocycloalkenyl” is a type of cycloalkenyl group where at least oneof the carbon atoms of the ring is substituted with a heteroatom suchas, but not limited to, nitrogen, oxygen, sulfur, or phosphorus. Thecycloalkenyl group and heterocycloalkenyl group can be substituted orunsubstituted. The cycloalkenyl group and heterocycloalkenyl group canbe substituted with one or more groups including, but not limited to,alkyl, alkoxy, alkenyl, alkynyl, aryl, heteroaryl, aldehyde, amino,carboxylic acid, ester, ether, halide, hydroxy, ketone, nitro, silyl,sulfo-oxo, sulfonyl, sulfone, sulfoxide, or thiol as described herein.

The term “cyclic group” is used herein to refer to either aryl groups,non-aryl groups (i.e., cycloalkyl, heterocycloalkyl, cycloalkenyl, andheterocycloalkenyl groups), or both. Cyclic groups have one or more ringsystems that can be substituted or unsubstituted. A cyclic group cancontain one or more aryl groups, one or more non-aryl groups, or one ormore aryl groups and one or more non-aryl groups.

The term “aldehyde” as used herein is represented by the formula —C(O)H.Throughout this specification “C(O)” is a short hand notation for C═O.

The terms “amine” or “amino” as used herein are represented by theformula NA¹A²A³, where A¹, A², and A³ can be, independently, hydrogen,an alkyl, halogenated alkyl, alkenyl, alkynyl, aryl, heteroaryl,cycloalkyl, cycloalkenyl, heterocycloalkyl, or heterocycloalkenyl groupdescribed above.

The term “carboxylic acid” as used herein is represented by the formula—C(O)OH. A “carboxylate” as used herein is represented by the formula—C(O)O⁻.

The term “ester” as used herein is represented by the formula —OC(O)A¹or —C(O)OA¹, where A¹ can be an alkyl, halogenated alkyl, alkenyl,alkynyl, aryl, heteroaryl, cycloalkyl, cycloalkenyl, heterocycloalkyl,or heterocycloalkenyl group described above.

The term “ether” as used herein is represented by the formula A¹OA²,where A¹ and A² can be, independently, an alkyl, halogenated alkyl,alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl, cycloalkenyl,heterocycloalkyl, or heterocycloalkenyl group described above.

The term “ketone” as used herein is represented by the formula A¹C(O)A²,where A¹ and A² can be, independently, an alkyl, halogenated alkyl,alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl, cycloalkenyl,heterocycloalkyl, or heterocycloalkenyl group described above.

The term “halide” as used herein refers to the halogens fluorine,chlorine, bromine, and iodine.

The term “hydroxyl” as used herein is represented by the formula —OH.

The term “nitrile” as used herein is represented by the formula —CN.

A “fluoroalkyl” as used herein is an alkyl group where one or more ofthe hydrogen atoms is substituted with a fluorine atom.

The term “nitrile terminated alkyl” as used herein is represented by theformula A′CN, where A¹ is an alkyl group as described above.

The term “trifluoromethyl terminated alkyl” as used herein isrepresented by the formula A¹CF₃, where A¹ is an alkyl group asdescribed above.

“A¹,” “A²,” “A³,” “A^(n),” etc., where n is some integer, as used hereincan, independently, possess one or more of the groups listed above. Forexample, if A¹ is a straight chain alkyl group, one of the hydrogenatoms of the alkyl group can optionally be substituted with a hydroxylgroup, an alkoxy group, an amine group, an alkyl group, a halide, andthe like. Depending upon the groups that are selected, a first group canbe incorporated within second group or, alternatively, the first groupcan be pendant (i.e., attached) to the second group. For example, withthe phrase “an alkyl group comprising an amino group,” the amino groupcan be incorporated within the backbone of the alkyl group.Alternatively, the amino group can be attached to the backbone of thealkyl group. The nature of the group(s) that is (are) selected willdetermine if the first group is embedded or attached to the secondgroup.

Reference will now be made in detail to specific aspects of thedisclosed materials, compounds, compositions, articles, and methods,examples of which are illustrated in the accompanying Examples andFigures.

Materials and Compositions

Certain materials, compounds, compositions, and components disclosedherein can be obtained commercially or readily synthesized usingtechniques generally known to those of skill in the art. For example,the starting materials and reagents used in preparing the disclosedcompounds and compositions are either available from commercialsuppliers such as Aldrich Chemical Co., (Milwaukee, Wis.), AcrosOrganics (Morris Plains, N.J.), Fisher Scientific (Pittsburgh, Pa.),Sigma (St. Louis, Mo.), or are prepared by methods known to thoseskilled in the art following procedures set forth in references such asFieser and Fieser's Reagents for Organic Synthesis, Volumes 1-17 (JohnWiley and Sons, 1991); Rodd's Chemistry of Carbon Compounds, Volumes 1-5and Supplementals (Elsevier Science Publishers, 1989); OrganicReactions, Volumes 1-40 (John Wiley and Sons, 1991); March's AdvancedOrganic Chemistry, (John Wiley and Sons, 4th Edition); and Larock'sComprehensive Organic Transformations (VCH Publishers Inc., 1989). Othermaterials, such as the ligands, disclosed herein can be obtained fromcommercial sources.

Method of Use

The solvent systems disclosed herein can be used to reduce acid gasesfrom a stream. Described herein is a method for reducing acid gas from astream, comprising contacting the stream with a solvent systemcomprising a glycerol derivative as described herein. The acid gasespresent in the stream can absorb and/or dissolve into the solvent systemcomprising the glycerol derivative. The acid gases present in the streamcan be reduced from the stream and increased in the solvent system. Thesolvent system and the stream can then be separated. The stream willhave a reduced amount of acid gas and the solvent system will have anincreased amount of acid gas.

The stream can be a liquid stream, including, for example, a solventwhere a chemical reaction is taking place, or a gaseous stream,including, for example, natural gas stream or a flue gas stream.

As used herein, acid gases can include undesirable gaseous componentsfound in a source and having a molecular weight lower than 150 g/mol.For example, the acid gases can have a molecular weight lower than 140g/mol, 130 g/mol, 120 g/mol, 110 g/mol, 100 g/mol, 90 g/mol, 80 g/mol,70 g/mol, 60 g/mol, 50 g/mol, 40 g/mol, 30 g/mol, 20 g/mol, or the like,where any of the stated values can form an upper or lower endpoint of arange. Examples of acid gases include CO₂, CO, COS, H₂S, SO₂, NO, N₂O,mercaptans, H₂O, O₂, H₂, N₂, Cl₂, volatile organic compounds, andmixtures of these. In some examples, the acid gas is selected from thegroup consisting of CO₂, H₂S, and SO₂. In some examples, the acid gas isa Lewis Acid, such as CO₂, H₂S, and SO₂. In some examples, the methodfor reducing acid gases from a stream can separate CO₂, H₂S, and SO₂from C₁-C₈ hydrocarbons (e.g., methane and propane). In some examples,the method for reducing acid gases from a stream can separate CO₂, H₂S,and SO₂ from a natural gas stream.

The method for reducing acid gases from a stream can include contactingthe stream with an effective amount of a solvent system as describedherein. In some embodiments, the solvent system comprises a glycerolderivative. For example, acid gases from a gas stream (e.g., a naturalgas stream or a flue gas stream) can be reduced according to thismethod.

In some examples, the method for reducing acid gases from a stream caninclude a liquid stream. For example, acid gases, such as CO₂ can beproduced as a byproduct of a chemical reaction. The acid gases caneither remain dissolved in the solvent of the chemical reaction orpressurize the headspace above the chemical reaction. The solvent systemcan contact the liquid stream (i.e., the solvent with dissolved acidgases) to remove the acid gases or the solvent system can contact thepressurized head space above the chemical reaction to remove the acidgases. In some examples, the solvent system can contact a water-gasshift reaction mixture to reduce CO₂.

In some examples, the solvent system can contact the stream in a hollowfiber membrane contactor. In some examples, the solvent system can beused within a hollow fiber membrane contactor. In some examples, thesolvent system can contact the stream in a vertical packed ortrayed-column. In some examples, the solvent system can contact thestream as in FIG. 1.

Further described herein is a method for sweetening a natural gas feedstream. The method comprises contacting the natural gas feed stream withan effective amount of a solvent system as described herein to form apurified natural gas feed stream and a gas-rich solvent system. Thepurified natural gas feed stream can then be separated from the gas-richsolvent system. In some embodiments, the acid gases are reduced from thegas-rich solvent system to regenerate the solvent system. The system canbe regenerated by heating or pressurizing the gas-rich solvent system.

Compositions

As noted, the disclosed methods comprise contacting a stream with asolvent system comprising a glycerol derivative. A glycerol derivativeis a compound that has glycerol as a backbone or core structuralcomponent.

Glycerol, 1,2,3-trihydroxypropane, is a simple polyol comprising apropane with three alcohol functional groups. Glycerol has a wide rangeof applications, including use as an organic solvent and as a sweetenerin foods. Glycerol is a byproduct of biodiesel production, and due tothe recent expansion of biodiesel product, there is a glut of glycerolin the market.

Unfortunately, glycerol is not an ideal choice for a solvent to dissolveCO₂ because of the relatively low solubility of CO₂ in glycerol whencompared to other alcohols of similar chain length (see Nunes et al.,Fluid Phase Equilibria 358 (2013) 105-107) and pure glycerol has a highviscosity at 25° C. of at least 1000 cP (see Segur and Oberstar, Ind.Eng. Chem. 43 (1951) 2117-2120). Although glycerol is a low cost liquidthat has a very low volatility (T_(b)=290° C.), it is too viscous in itspure form (μ>1000 cP at 25° C.) to be considered as a viable physicalsolvent for CO₂ absorption. Dilution with H₂O to reduce viscosity wouldalso likely have a detrimental impact on CO₂ solubility inglycerol-containing solutions.

However, disclosed herein are lower viscosity glycerol derivatives,which can allow the glycerol derivatives to be used as physical solventsfor the absorption of CO₂ from streams.

In some aspects, disclosed herein are glycerol derivatives, which can beused to reduce the amount of acidic gases from streams. In someexamples, the glycerol derivative can be represented by Formula I.

wherein R¹, R², and R³ can be independently selected from the groupconsisting of substituted or unsubstituted C₁₋₂₀ alkyl, substituted orunsubstituted C₂₋₂₀ alkenyl, substituted or unsubstituted C₂₋₂₀ alkynyl,substituted or unsubstituted cycloalkyl, substituted or unsubstitutedaryl, substituted or unsubstituted thio, substituted or unsubstitutedalkoxyl, substituted or unsubstituted aryloxyl, C₂₋₂₀ fluoroalkyl,C₂-C₂₀ trifluoromethyl terminated alkyl, and C₂₋₂₀ nitrile terminatedalkyl.

In some examples, R¹, R², and R³ can be independently selected from thegroup consisting of substituted or unsubstituted C₁₋₂₀ alkyl,substituted or unsubstituted alkoxyl, and C₂-C₂₀ trifluoromethylterminated alkyl. In some examples, R¹, R², and R³ can be independentlyselected from the group consisting of C₁₋₂₀ alkyl substituted with oneor more ethers, C₁₋₂₀ alkyl substituted with one or more C₁₋₅ alkyl,C₁₋₂₀ alkyl substituted with one or more halogen, C₁₋₂₀ alkylsubstituted with one or more amine, C₁₋₂₀ alkyl substituted with one ormore hydroxyl, C₁₋₂₀ alkyl substituted with one or more C₁₋₅ alkoxy,C₁₋₂₀ alkoxy substituted with one or more ethers, C₁₋₂₀ alkoxysubstituted with one or more C₁₋₅ alkyl, C₁₋₂₀ alkoxy substituted withone or more halogen, C₁₋₂₀ alkoxy substituted with one or more amine,C₁₋₂₀ alkoxy substituted with one or more hydroxyl, and C₁₋₂₀ alkoxysubstituted with one or more C₁₋₅ alkoxy.

In some examples, the glycerol derivative can be selected from the groupconsisting of 1,2,3-trimethoxypropane, 1,2,3-triethoxypropane,1,2,3-tri(2-methoxyethyl)propane, and1,2,3-tris(2,2,2-trifluoroethoxy)propane.

In some examples, the glycerol derivative is 1,2,3-trimethoxypropane.

In some examples, the glycerol derivative has a lower viscosity thanpure glycerol. In some examples, the glycerol derivative has a viscosityat or below 1000 cP at 25° C., at or below 900 cP at 25° C., at or below800 cP at 25° C., at or below 700 cP at 25° C., at or below 600 cP at25° C., at or below 500 cP at 25° C., at or below 400 cP at 25° C., ator below 300 cP at 25° C., at or below 200 cP at 25° C., at or below 100cP at 25° C., at or below 90 cP at 25° C., at or below 80 cP at 25° C.,at or below 70 cP at 25° C., at or below 60 cP at 25° C., at or below 50cP at 25° C., at or below 40 cP at 25° C., at or below 30 cP at 25° C.,at or below 20 cP at 25° C., at or below 10 cP at 25° C., at or below 9cP at 25° C., at or below 8 cP at 25° C., at or below 7 cP at 25° C., ator below 6 cP at 25° C., at or below 5 cP at 25° C., at or below 4 cP at25° C., at or below 3 cP at 25° C., at or below 2.5 cP at 25° C., at orbelow 2 cP at 25° C., at or below 1.5 cP at 25° C., or at or below 1 cPat 25° C. When viscosity is discussed herein, all viscosity values aretested according to Example 5.

Solvent System

Also disclosed herein is a solvent system comprises a glycerolderivative. In some examples, a solvent system can comprise a glycerolderivative and an organic solvent. In some examples, a solvent systemcan comprise a glycerol derivative and optionally an organic solvent orwater. The organic solvent can be selected from the group consisting ofmethanol, ethanol, 1-propanol, 2-propanol, diglyme, DMPEG,dichloromethane, chloroform, ethyl acetate, tetrahydrofuran, acetone,acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, glycolsolvents, acetone, butanol, another suitable organic solvent, andmixtures thereof.

In some examples, the solvent system comprises at least 5%, at least10%, at least 15%, at least 20%, at least 25%, at least 30%, at least35%, at least 40%, at least 45%, at least 50%, at least 55%, at least60%, at least 65%, at least 70%, at least 75%, at least 80%, at least85%, at least 90%, at least 95%, at least 96%, at least 97%, at least98%, at least 99%, or at least 99.5% of the glycerol derivative byvolume.

In some examples, disclosed herein is a solvent system for reducing acidgas from a stream comprising a glycerol derivative and acid gas.

The examples below are intended to further illustrate certain aspects ofthe methods and compositions described herein, and are not intended tolimit the scope of the claims.

EXAMPLES

The following examples are set forth below to illustrate the methods andresults according to the disclosed subject matter. These examples arenot intended to be inclusive of all aspects of the subject matterdisclosed herein, but rather to illustrate representative methods andresults. These examples are not intended to exclude equivalents andvariations of the present invention, which are apparent to one skilledin the art.

Efforts have been made to ensure accuracy with respect to numbers (e.g.,amounts, temperature, etc.) but some errors and deviations should beaccounted for. Unless indicated otherwise, parts are parts by weight,temperature is in ° C. or is at ambient temperature, and pressure is ator near atmospheric. There are numerous variations and combinations ofreaction conditions, e.g., component concentrations, temperatures,pressures and other reaction ranges and conditions that can be used tooptimize the product purity and yield obtained from the describedprocess. Only reasonable and routine experimentation will be required tooptimize such process conditions.

Glycerol (>99.7%) was purchased from BDH. Dimethyl sulfate (DMS) (>99%)was purchased from Sigma-Aldrich. Tert-butyl ammonium hydrogen sulfate(TBAHS) (98%) was purchased from Baker. CaH₂ (90-95%) and diglyme (99%)were purchased from Alfa Aesar. NaOH (pellets, ACS Grade) was purchasedfrom VWR. Research grade CO₂ was purchased from Airgas (Radnor, Pa.USA).

Example 1: Synthesis of 1,2,3-Trimethoxypropane

1,2,3-Trimethoxypropane (1,2,3-TMP) was synthesized from glycerol, NaOHand dimethyl sulfate (DMS) in the presence of (n-Bu)₄NHSO₄, or TBAHS, aphase transfer catalyst, in the absence of any additional solventaccording to Scheme 1.

In a 2 L double walled glass reactor equipped with a cooling system(water stream) and a mechanical anchor Teflon stirrer, glycerol (139 g,111 mL, 1.51 mol, 1 eq.), 101 g of NaOH (2.53 mol, 1.65 eq.) and 5.28 gof (n-Bu)₄NHSO₄(TBAHS, 15.6 mmol, 10 mol %) were successively introducedin small portions under stirring. The mixture was then stirred at roomtemperature for 30 min until the medium became more homogeneous. Aftercooling down the reactor to 15° C. with a cold water stream, dimethylsulfate (DMS, 166 g, 125 mL, 1.30 mol, 0.85 eq) was carefully addeddropwise to the reaction medium. Next, the rest of NaOH was slowly added(101 g, 2.53 mol, 1.65 eq) before adding the remaining DMS dropwise (166g, 125 mL, 1.30 mol, 0.85 eq). The basicity of the mixture was thenchecked by pH measurement, and the medium was vigorously stirred at roomtemperature for 16 h.

Following the reaction, pentane (1000 mL) was added to the solids andthe slurry was mixed for several hours via mechanical mixing. The solidswere then separated by vacuum filtration, and the filtrate volume wasreduced to ˜150 mL via rotary evaporation, followed by distillation of1,2,3-TMP over CaH₂. Using Karl-Fisher titration, the H₂O content of1,2,3-TMP post-distillation was determined to be >1000 ppm, which wasreduced to ˜75 ppm when stored in crimped septum vials over activated 3Å carbon molecular sieves. ¹H and ¹³C NMR characterization data andspectra were consistent with the synthesis of 1,2,3-TMP.

Example 2: Prophetic Examples of Other Glycerol Derivatives

Other glycerol derivatives can be synthesized using similar reactionprotocols to Example 1. For example, glycerol derivatives can besynthesized using alkylation reaction protocols, to synthesize thederivatives in Formula I.

In Formula I, R¹, R², and R³ can be independently selected from alkyl oralkyl ether functional group. These compounds can be synthesized in analkylation reaction with the appropriate dialkyl sulfate. For example, asimilar reaction to Example 2 can be performed with glycerol and diethylsulfate to synthesize 1,2,3-triethoxypropane. In one example, analkylation reaction can be used to synthesize 1,2,3-triisopropoxypropaneby reacting isopropyl tosylate with glycerol.

Other alkylating agents may be used to produce a derivative as inFormula I. Some examples include methyl iodide, ethyl bromide, ethylchloride, diethyl sulfate, dipropyl sulfate, 1-chlorobutane,1-chloropropane, 2-chloroethyl methyl ether, 2-chloroethyl ethyl ether,1-bromobutane, and 2,2,2-Trifluoroethyl 4-toluenesulfonate.

Example 3: Density Measurements

Density data were measured using a Mettler-Toledo DM45 DeltaRangedensity meter that operates using electromagnetically inducedoscillation of a glass U-form tube, with automatic compensation forchanges in atmospheric pressure. The density meter can measure samplesin the liquid phase with densities between 0-3 g/cm³ and requires aminimum sample size of 1.2 cm³. Density measurements are accurate within±0.00005 g/cm³ for all operating temperatures. Densities of 1,2,3-TMPwere recorded at 10° C. intervals from 20-80° C. and available in Table1.

TABLE 1 Density (g/cm³) of 1,2,3-TMP at various temperatures (° C.)Temp. (° C.) 20 30 40 50 60 70 80 Density 0.94169 0.93171 0.921680.91155 0.90133 0.89099 0.88050 (g/cm³)

Example 4: Viscosity Measurements

Viscosity data were measured using a Brookfield DV-II+ Pro viscometer.The viscosity is based on a torque value and shear rate of a spindle incontact with a specified amount of fluid. For these experiments, the“ULA” spindle and jacketed sample cell was used because viscosities were<25 cP. This configuration requires a minimum fluid volume of 16 cm³.The accuracy of the viscometer is ±1% of the reading for torquemeasurements with a repeatability of ±0.2% of the reading. The viscosityof 1,2,3-TMP was measured at 10 temperature values between 19.8° C. and80.2° C. The temperature was controlled by a Brookfield TC-602Pcirculating bath with a temperature stability of ±0.01° C. Values forviscosity are available in Table 2.

TABLE 2 Viscosity (cP) of 1,2,3-TMP at various temperatures (° C.) Temp.(° C.) 20 30 40 50 60 70 80 Viscosity 1.07 1.05 1.03 1.01 0.95 0.89 0.83(cP)

Example 5: Gas Solubility in Glycerol Derivatives

As shown in FIG. 1, a glass pressure tube with threaded fitting glassvessel was filled with a known mass of solvent, a magnetic stir bar wasadded, and the vessel sealed with a PTFE threaded cap. The apparatus wasplaced in a tall-form 400 mL beaker filled with water. Pressure wasmonitored by a pressure sensor. A temperature-controlled hotplate withmagnetic stirring was employed for heating and stirring of the waterfilled beaker. Temperature was measured with a thermocouple connected ina feedback loop to a hot plate with magnetic stirring capabilities.

The loaded vessel was connected to vacuum/gas/vent lines via the 3-wayvalve. First, the system was degassed at 30° C. via a vacuum pump toremove residual air from the headspace. After the pressure in the cellmaintained a constant value while under vacuum, the initial mass of thesystem was recorded. Next, CO₂ at an absolute pressure of ˜2 atm wasintroduced via 3-way valve, until the system came to equilibrium (asdetermined by readings that deviated no more than ±2 mm Hg for >20 min).The pressure was recorded, the vessel disconnected from the pressuresensor, removed from the water bath, dried, and the mass of the vesselrecorded. The increase in the mass of the vessel relative to the initialstate can be taken as the total mass of CO₂ added to the vesseldistributed between the vapor and liquid phases.

The vessel was then returned to the water bath, reconnected to thepressure sensor and the bath heated to 45° C. while stirring. The systempressure was allowed to equilibrate at 45° C. and the pressure recorded.The process was repeated again at 60° C. and 75° C. After this procedurewas completed, the system was cooled to 30° C., and the system wasexposed to CO₂ at an absolute pressure of ˜4 atm until equilibrium wasreached, with the new mass of the system recorded. Equilibrium pressureswere recorded at the same temperature intervals. The process wasrepeated a final time starting at 30° C. and an absolute pressure of CO₂at ˜6 atm.

Measuring the mass increase of the system allows for the number of totalmoles of CO₂ in the system to be calculated via Eqn. 1, where n_(CO2) isthe number of moles of CO₂ present in the system at a given T,Pequilibrium, m_(i) is the measured mass of the system at thisequilibrium in g, m₀ is the initial mass of the degassed system in g,and MW is the molecular weight of CO₂ (44.01 g/mol)

$\begin{matrix}{n_{{CO}\; 2} = \frac{{mi} - m_{o}}{MW}} & (1)\end{matrix}$

Partitioning of CO₂ between the liquid and vapor phases can becalculated using Eqn. 2, where P is the absolute pressure in, z is thecompressibility factor (as calculated from NIST REFPROP), n_(vapor) isthe number of moles of CO₂ in the headspace, R is the gas constant, T isthe absolute temperature, V_(total) is the volume of the empty reactorminus the known volume of the stir bar, V_(TMP) is the volume of thesolvent as calculated from the mass, temperature and density, V_(crit)is the molar solubilized volume of CO₂ (taken as the critical volume, 34cm³/mol), and nCO₂ is the total number of moles of CO₂ in the system ascalculated from the mass balance in Eqn. 1.

$\begin{matrix}{P = \frac{z*n_{vapor}*R*T}{\left( {V_{total} - V_{TMP} - {V_{crit}*\left( {{{n{CO}}\; 2} - n_{vapor}} \right)}} \right)}} & (2)\end{matrix}$

Solving for n_(vapor) at each equilibrium pressure gives the number ofmoles of CO₂ absorbed into the 1,2,3-TMP and the mole fraction of CO₂ inthe solution can be determined via Eqn. 3.n _(CO) ₂ ^(L) =n _(CO) ₂ −n _(CO) ₂ ^(V)  (3)

The mole fractions of CO₂ (x^(L) _(CO2)) in the liquid phase at eachgiven T, P condition is calculated from Eqn. 4:

$\begin{matrix}{x_{{CO}_{2}}^{L} = \frac{n_{{CO}\; 2}^{L}}{n_{{CO}\; 2}^{L} + n_{S}}} & (4)\end{matrix}$where n_(S) is the moles of solvent (1,2,3-TMP or diglyme) originallyadded to the vessel.

The Henry's constant (H_(CO2,1)(atm)) of CO₂ at each temperature, whereCO₂ is the solute and 1=solvent (1,2,3-TMP or diglyme) was calculatedfrom the inverse linear relationship in Eqn. 5:

$\begin{matrix}{{H_{{CO}_{2},1}({atm})} = \frac{P({atm})}{x_{{CO}_{2}}^{L}}} & (5)\end{matrix}$

In FIG. 2, CO₂ solubility was tested in diglyme and 1,2,3-TMP. Thephysical solubility of CO₂ in 1,2,3-TMP is greater than the physicalsolubility in diglyme, which was tested to mimic commercially utilizedDMPEG. FIGS. 3A and 3B show the solubility of CO₂ in 1,2,3-TMP ordiglyme as a function of temperature. Tables 3 and 4 show the solubilityof CO₂ in 1,2,3-TMP and diglyme respectively.

TABLE 3 CO₂ solubility in 1,2,3-TMP. Temp H S_(v) S_(m) (° C.) (atm)(cm³ (STP) cm⁻³ atm⁻¹) (mol kg⁻¹ atm⁻¹) 30 44.2 +/− 0.4 3.88 +/− 0.190.186 +/− 0.009 45 58.3 +/− 0.9 2.89 +/− 0.14 0.141 +/− 0.007 60 72.4+/− 1.9 2.26 +/− 0.14 0.112 +/− 0.007 75 87.2 +/− 3.2 1.83 +/− 0.130.092 +/− 0.007

TABLE 4 CO₂ solubility in diglyme. Temp H S_(v) S_(m) (° C.) (atm) (cm³(STP) cm⁻³ atm⁻¹) (mol kg⁻¹ atm⁻¹) 30 42.1 +/− 0.3 4.02 +/− 0.11 0.192+/− 0.005 45 54.7 +/− 0.2 3.04 +/− 0.07 0.148 +/− 0.004 60 68.8 +/− 1.52.36 +/− 0.10 0.117 +/− 0.005 75 83.8 +/− 0.8 1.91 +/− 0.06 0.096 +/−0.003

Example 6: Comparison of Glycerol Derivatives to Existing Technologies

TABLE 5 Comparison of Physical and Chemical Properties 1,2,3-TMP DiglymeDMPEGs Commercial Process name N/A N/A Selexol Viscosity (cP) 1.05 1.25.8 Specific Gravity (kg/m³) 937 939 1030 Molecular Weight (g/mol)134.18 134.18 ~280 Vapor Pressure (Torr) 2.62 1.20 0.00073 FreezingPoint (° C.) TBD −64 −28 Boiling Point (at 760 Torr) ~140 162 275Maximum Operating Boiling Point Boiling Point 175 Temperature CO₂Solubility (ft³/US gal) 0.527 0.546 0.485 CO₂/CH₄ TBD TBD 15 H₂S/CO₂ TBD5.8 8.82 H₂O miscible? Yes Yes Yes

The compositions and methods of the appended claims are not limited inscope by the specific compositions and methods described herein, whichare intended as illustrations of a few aspects of the claims and anycompositions and methods that are functionally equivalent are intendedto fall within the scope of the claims. Various modifications of thecompositions and methods in addition to those shown and described hereinare intended to fall within the scope of the appended claims. Further,while only certain representative compositions and methods disclosedherein are specifically described, other combinations of thecompositions and methods also are intended to fall within the scope ofthe appended claims, even if not specifically recited. Thus, acombination of steps, elements, components, or constituents may beexplicitly mentioned herein; however, other combinations of steps,elements, components, and constituents are included, even though notexplicitly stated.

It will be appreciated that variants of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be combined intomany other different systems or applications. Various presentlyunforeseen or unanticipated alternatives, modifications, variations, orimprovements therein may be subsequently made by those skilled in theart which are also intended to be encompassed by the following claims.

What is claimed is:
 1. A method of reducing acid gas from a stream,comprising contacting the stream with a solvent system comprising aglycerol derivative, wherein the glycerol derivative has the followingstructure:

wherein R¹, R² and R³ are independently selected from the groupconsisting of C₁₋₂₀ alkyl, C₂₋₂₀ alkenyl, C₂₋₂₀ alkynyl, cycloalkyl,aryl, thio, alkoxyl, aryloxyl, C₂₋₂₀ fluoroalkyl, C₂-C₂₀ trifluoromethylterminated alkyl, and C₂₋₂₀ nitrile terminated alkyl, any of which isoptionally substituted with one or more substituents selected from thegroup consisting of ether, C₁-C₅ alkyl, halogen, amine, and C₁-C₅alkoxy; with the proviso that at least one of R¹, R², and R³ is notC(O)CH₃.
 2. The method of claim 1, wherein R′, R² and R³ areindependently selected from the group consisting of C₁₋₂₀ alkyl, alkoxy,and C₂-C₂₀ trifluoromethyl terminated alkyl, any of which is optionallysubstituted with one or more substituents selected from the groupconsisting of ether, C₁-C₅ alkyl, halogen, amine, and C₁-C₅ alkoxy. 3.The method of claim 1, wherein the viscosity of the glycerol derivativeis at or below 5 cP at 25° C.
 4. The method of claim 1, wherein theglycerol derivative is selected from the group consisting of1,2,3-trimethoxypropane, 1,2,3-triethoxypropane, and1,2,3-tris(2,2,2-trifluoroethoxy)propane.
 5. The method of claim 1,wherein the acid gas is selected from the group consisting of carbondioxide, sulfur dioxide, hydrogen sulfide, and mixtures thereof.
 6. Themethod of claim 1, wherein the stream is selected from the groupconsisting of natural gas, byproducts of a chemical reaction, andpost-combustion flue gas.
 7. The method of claim 1, wherein the streamcomprises the gaseous products produced from a water-gas shift reaction.8. The method of claim 1, wherein the acid gas is removed from thestream through absorption into the glycerol derivative.
 9. The method ofclaim 1, wherein the solvent system comprises at least 50% of theglycerol derivative by volume.
 10. The method of claim 1, wherein thesolvent system contacts the stream in a hollow fiber membrane contactor.11. The method of claim 1, wherein R¹, R², and R³ are independentlyselected from the group consisting of unsubstituted C₁₋₂₀ alkyl,unsubstituted C₂₋₂₀ alkenyl, unsubstituted C₂₋₂₀ alkynyl, unsubstitutedcycloalkyl, unsubstituted aryl, unsubstituted thio, unsubstitutedalkoxyl, unsubstituted aryloxyl, unsubstituted C₂₋₂₀ fluoroalkyl,unsubstituted C₂-C₂₀ trifluoromethyl terminated alkyl, and unsubstitutedC₂₋₂₀ nitrile terminated alkyl.
 12. The method of claim 1, wherein R¹,R² and R³ are independently selected from the group consisting ofunsubstituted C₁₋₂₀ alkyl, unsubstituted alkoxy, and unsubstitutedC₂-C₂₀ trifluoromethyl terminated alkyl.
 13. The method of claim 1,wherein R¹, R², and R³ are independently selected from the groupconsisting of —CH₃, —CH₂CH₃, —CH₂CF₃, and —CH₂CH₂OCH₃.
 14. The method ofclaim 1, wherein R¹, R², R³ are not all the same.
 15. A method forsweetening a natural gas feed stream, comprising contacting the naturalgas feed stream, wherein the natural gas feed stream comprises acidgases, with a solvent system comprising a glycerol derivative, whereinthe glycerol derivative has the following structure:

wherein R¹, R² and R³ are independently selected from C₁₋₂₀ alkyl, C₂₋₂₀alkenyl, C₂₋₂₀ alkynyl, cycloalkyl, aryl, thio, alkoxyl, aryloxyl, C₂₋₂₀fluoroalkyl, C₂-C₂₀ trifluoromethyl terminated alkyl, and C₂₋₂₀ nitrileterminated alkyl, any of which is optionally substituted with one ormore substituents selected from the group consisting of ether, C₁-C₅alkyl, halogen, amine, and C₁-c₅ alkoxy; with the proviso that at leastone of R¹, R², and R³ is not C(O)CH₃.
 16. The method of claim 15,wherein R¹, R² and R³ are independently selected from C₁₋₂₀ alkyl,alkoxy, and C₂-C₂₀ trifluoromethyl terminated alkyl, any of which isoptionally substituted with one or more substituents selected from thegroup consisting of ether, C₁-C₅ alkyl, halogen, amine, and C₁-C₅alkoxy.
 17. The method of claim 15, wherein the viscosity of theglycerol derivative is at or below 5 cP at 25° C.
 18. The method ofclaim 15, wherein the glycerol derivative is selected from the groupconsisting of 1,2,3-trimethoxypropane, 1,2,3-triethoxypropane, and1,2,3-tris(2,2,2-trifluoroethoxy)propane.
 19. The method of claim 15,wherein the acid gas is selected from the group consisting of carbondioxide, sulfur dioxide, hydrogen sulfide, and mixtures thereof.
 20. Themethod of claim 15, wherein the acid gas is removed from the natural gasfeed stream through absorption into the glycerol derivative.
 21. Themethod of claim 15, wherein the solvent system comprises at least 50% ofthe glycerol derivative by volume.
 22. The method of claim 15, whereinthe solvent system is used within a hollow fiber membrane contactor. 23.The method of claim 15, wherein R¹, R², and R³ are independentlyselected from the group consisting of unsubstituted C₁₋₂₀ alkyl,unsubstituted C₂₋₂₀ alkenyl, unsubstituted C₂₋₂₀ alkynyl, unsubstitutedcycloalkyl, unsubstituted aryl, unsubstituted thio, unsubstitutedalkoxyl, unsubstituted aryloxyl, unsubstituted C₂₋₂₀ fluoroalkyl,unsubstituted C₂-C₂₀ trifluoromethyl terminated alkyl, and unsubstitutedC₂₋₂₀ nitrile terminated alkyl.
 24. The method of claim 15, wherein R¹,R² and R³ are independently selected from the group consisting ofunsubstituted C₁₋₂₀ alkyl, unsubstituted alkoxy, and unsubstitutedC₂-C₂₀ trifluoromethyl terminated alkyl.
 25. The method of claim 15,wherein R¹, R², and R³ are independently selected from the groupconsisting of —CH₃, —CH₂CH₃, —CH₂CF₃, and —CH₂CH₂OCH₃.
 26. The method ofclaim 15, wherein R¹, R², R³ are not all the same.